1. Field of the Invention
The present invention relates to an electric device containing a battery that can be used by repeating charging/discharging, and particularly it relates to an electric device that can accommodate capacity deterioration of the battery.
2. Prior Art
Various electric devices including information terminals such as notebook-type personal computers (notebook PCs), PDAs (Personal Digital Assistants), MD (Mini Disc) drives and video cameras, are supplied with power not only directly through a commercial main but also from a battery that can be used by repeating charging/discharging. Nickel-hydrogen batteries or nickel-cadmium batteries are employed as batteries used in the electric devices because of their large capacity and low price. The batteries used in the electric devices also include lithium-ion batteries, which have higher energy density per unit weight than the nickel-cadmium batteries, and lithium-polymer batteries, which use solid polymer instead of liquid electrolyte.
Users strongly desire to know accurately a life of a battery such as nickel-hydrogen battery, nickel-cadmium battery, lithium-ion battery or lithium-polymer battery, because operating time of the battery decreases after the life of the battery has expired. Accordingly, some conventional electric appliances indicate data such as voltage, current, and capacity of its battery to inform a user of time to exchange the battery.
Problems to be Solved by the Invention:
However, since conventional indication of voltage, current and capacity (%) only shows basic data, it is difficult for a user to properly determine a presence of abnormality in the battery or an exchange time of the battery.
Deterioration of a battery can be known from Full Charge Capacity (total capacity). It is possible to know a deterioration degree of a battery by monitoring a change in Full Charge Capacity of the battery. Conventionally, however, it has not been possible to exactly monitor Full Charge Capacity unless the battery, after charged to 100% of capacity, discharges completely to about 0% of capacity (3%, for example). Thus, an exact deterioration degree of the battery can be only known after the battery charging followed by complete discharging. Accordingly, for example, it may take about half a day to get a deterioration degree of a battery in a device, and thus it takes time and effort.
Furthermore, when Full Charge Capacity of a battery is monitored and its deterioration degree is notified to a user, the notified deterioration degree cannot be accurate unless complete discharging is performed just before the notification. Users seldom use batteries to a completely discharged state. Therefore, in order to obtain an exact deterioration degree, it is required to instruct a user to use a battery by charging to 100% capacity and completely discharging. However, usability of a device is not good if complete discharging is required to measure a deterioration degree of its battery.
The present invention solves the technical problems described above.